Non-mammalian vertebrate models and the endocannabinoid system: Relationships with gonadotropin-releasing hormone

Endocannabinoids, via cannabinoid receptors (CB1 and CB2), affect reproductive functions at both local and central level. Due to the high complexity of the endocannabinoid system, to the widespread distribution outside the nervous system and to the high degree of evolutionary conservation, a deep CB1 molecular characterization among species may be useful to elucidate the activity of endocannabinoids at multiple levels. In this review we report CB1 characterization in non-mammalian animal models and, in particular, in the anuran amphibian, the frog, Rana esculenta; we also describe its expression during the annual sexual cycle. Moreover, since reproductive functions are under control of gonadotropin releasing hormone (GnRH), cb1 mRNA and protein expression profile in the forebrain has been compared to those of GnRH-I, the mammalian form primarily involved in gonadotropin release.